1. Field of the Invention
The present invention generally relates to the art of avionics, and more specifically to a combiner assembly for a head-up-display (HUD) including a linkage mechanism which enables the combiner to be moved to and locked in an upper storage position or a lower operating position.
2. Description of the Related Art
A HUD provides a pilot with aircraft flight status information superimposed on a direct visual view through the front window. The pilot is freed from having to constantly shift sight from the window to dials in the cockpit in the conventional manner. This capability can provide a crucial advantage during high speed flight maneuvers, and during take-offs and landings in which conditions can deteriorate rapidly.
As illustrated in FIG. 1, a HUD display 10 to which the present invention relates includes a holographic mirror combiner 12 which is located between a pilot 14 and a front window 16 of an aircraft in a lower operating position as illustrated in solid line. A flight information or HUD image is projected onto the combiner 12 by a projector 18 which is mounted on a fuselage 20 of the aircraft above the pilot 14.
The combiner 12 is transparent to the pilot's view through the window 16, but reflects the image from the projector 18 such that it is visible by the pilot 14 superimposed on the direct view. The HUD image can be a radar display of the ground below the aircraft, or an information display including symbols designating flight parameters such as horizon, course, heading, altitude, airspeed, etc.
The combiner 12 is supported by a linkage mechanism 22 embodying the present invention, and is movable by the pilot 14 between the lower operating position and an upper storage position as illustrated in broken line. The combiner 12 is clear of the pilot's field of view in the storage position. The pilot 14 is seated sufficiently rearward of the combiner 12 such that the combiner 12 will not strike the pilot 14 while it is being moved between the operating and storage positions.
A prior art mechanism which performs the function of the present mechanism 22 is disclosed in U.S. Pat. No. 4,775,218, entitled "COMBINER ALIGNMENT DETECTOR FOR HEAD UP DISPLAY SYSTEM" issued Oct. 4, 1988 to R. Wood et al, and includes a pivotal bracket which supports the combiner.
Detent mechanisms including spring loaded, tapered pins which fit into tapered holes are provided for holding the bracket and combiner in the operating or stowed position. The detent mechanisms require precision machining, are subject to wear and are not dependable in that the combiner must often be bumped to fully engage the detents.
U.S. Pat. No. 4,664,475, entitled "COMBINER MOUNTING AND STOWAGE MECHANISM", issued May 12, 1987 to J. Ferrer, discloses a four bar linkage for moving a combiner between an upper operating position and a lower stowed position. The combiner is supported by two movable links, and the linkage is moved between the two positions by a slide arrangement.
The slide is held in the operating position by a detent. This arrangement is disadvantageous in that the slide and detent are subject to wear which causes the mechanism to become progressively loose and eventually fail to securely hold the combiner in the operating position.